Mass spectrometers are devices which vaporize and ionize a sample and then determine the mass to charge ratios of the collection of ions formed. One well known mass analyzer is the time-of-flight mass spectrometer (TOFMS), in which the mass to charge ratio of an ion is determined by the amount of time required for that ion to be transmitted under the influence of pulsed electric fields from the ion source to a detector. The spectral quality in TOFMS reflects the initial conditions of the ion beam prior to acceleration into a field free drift region. Specifically, any factor which results in ions of the same mass having different kinetic energies and/or being accelerated from different points in space will result in a degradation of spectral resolution, and thereby, a loss of mass accuracy. Matrix assisted laser desorption ionization (MALDI) is a well-known method to produce gas phase biomolecular ions for mass spectrometric analysis. The development of delayed extraction (DE) for MALDI-TOF has made high resolution routine for MALDI-based instruments. In DE-MALDI, a short delay is added between the ionization event, triggered by the laser, and the application of the accelerating pulse to the TOF source region. The fast (i.e., high-energy) ions will travel farther than the slow ions thereby transforming the energy distribution upon ionization to a spatial distribution upon acceleration (in the ionization region prior to the extraction pulse application).
See U.S. Pat. Nos. 5,625,184, 5,627,369 and 5,760,393. See also, Wiley et al., Time-of-flight mass spectrometer with improved resolution, Review of Scientific Instruments vol. 26, no. 12, pp. 1150-1157 (2004); M. L. Vestal, Modern MALDI time-of-flight mass spectrometry, Journal of Mass Spectrometry, vol. 44, no. 3, pp. 303-317 (2009); Vestal et al., Resolution and mass accuracy in matrix-assisted laser desorption ionization-time-of-flight, Journal of the American Society for Mass Spectrometry, vol. 9, no. 9, pp. 892-911 (1998); and Vestal et al., High Performance MALDI-TOF mass spectrometry for proteomics, International Journal of Mass Spectrometry, vol. 268, no. 2, pp. 83-92 (2007). The contents of these documents are hereby incorporated by reference as if recited in full herein.